/*      $OpenBSD: bs_ber.c,v 1.13 2025/03/28 12:13:03 tb Exp $  */
/*
 * Copyright (c) 2014, Google Inc.
 *
 * Permission to use, copy, modify, and/or distribute this software for any
 * purpose with or without fee is hereby granted, provided that the above
 * copyright notice and this permission notice appear in all copies.
 *
 * THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
 * WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
 * MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY
 * SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
 * WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN ACTION
 * OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF OR IN
 * CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
 */

#include <stdint.h>
#include <string.h>

#include "bytestring.h"

/*
 * kMaxDepth is a just a sanity limit. The code should be such that the length
 * of the input being processes always decreases. None the less, a very large
 * input could otherwise cause the stack to overflow.
 */
static const unsigned int kMaxDepth = 2048;

/* Non-strict version that allows a relaxed DER with indefinite form. */
static int
cbs_nonstrict_get_any_asn1_element(CBS *cbs, CBS *out, unsigned int *out_tag,
    size_t *out_header_len)
{
        return cbs_get_any_asn1_element_internal(cbs, out,
            out_tag, out_header_len, 0);
}

/*
 * cbs_find_indefinite walks an ASN.1 structure in |orig_in| and sets
 * |*indefinite_found| depending on whether an indefinite length element was
 * found. The value of |orig_in| is not modified.
 *
 * Returns one on success (i.e. |*indefinite_found| was set) and zero on error.
 */
static int
cbs_find_indefinite(const CBS *orig_in, char *indefinite_found,
    unsigned int depth)
{
        CBS in;

        if (depth > kMaxDepth)
                return 0;

        CBS_init(&in, CBS_data(orig_in), CBS_len(orig_in));

        while (CBS_len(&in) > 0) {
                CBS contents;
                unsigned int tag;
                size_t header_len;

                if (!cbs_nonstrict_get_any_asn1_element(&in, &contents, &tag,
                    &header_len))
                        return 0;

                /* Indefinite form not allowed by DER. */
                if (CBS_len(&contents) == header_len && header_len > 0 &&
                    CBS_data(&contents)[header_len - 1] == 0x80) {
                        *indefinite_found = 1;
                        return 1;
                }
                if (tag & CBS_ASN1_CONSTRUCTED) {
                        if (!CBS_skip(&contents, header_len) ||
                            !cbs_find_indefinite(&contents, indefinite_found,
                            depth + 1))
                                return 0;
                }
        }

        *indefinite_found = 0;
        return 1;
}

/*
 * is_primitive_type returns true if |tag| likely a primitive type. Normally
 * one can just test the "constructed" bit in the tag but, in BER, even
 * primitive tags can have the constructed bit if they have indefinite
 * length.
 */
static char
is_primitive_type(unsigned int tag)
{
        return (tag & 0xc0) == 0 &&
            (tag & 0x1f) != (CBS_ASN1_SEQUENCE & 0x1f) &&
            (tag & 0x1f) != (CBS_ASN1_SET & 0x1f);
}

/*
 * is_eoc returns true if |header_len| and |contents|, as returned by
 * |cbs_nonstrict_get_any_asn1_element|, indicate an "end of contents" (EOC)
 * value.
 */
static char
is_eoc(size_t header_len, CBS *contents)
{
        const unsigned char eoc[] = {0x0, 0x0};

        return header_len == 2 && CBS_mem_equal(contents, eoc, 2);
}

/*
 * cbs_convert_indefinite reads data with DER encoding (but relaxed to allow
 * indefinite form) from |in| and writes definite form DER data to |out|. If
 * |squash_header| is set then the top-level of elements from |in| will not
 * have their headers written. This is used when concatenating the fragments of
 * an indefinite length, primitive value. If |looking_for_eoc| is set then any
 * EOC elements found will cause the function to return after consuming it.
 * It returns one on success and zero on error.
 */
static int
cbs_convert_indefinite(CBS *in, CBB *out, char squash_header,
    char looking_for_eoc, unsigned int depth)
{
        if (depth > kMaxDepth)
                return 0;

        while (CBS_len(in) > 0) {
                CBS contents;
                unsigned int tag;
                size_t header_len;
                CBB *out_contents, out_contents_storage;

                if (!cbs_nonstrict_get_any_asn1_element(in, &contents, &tag,
                    &header_len))
                        return 0;

                out_contents = out;

                if (CBS_len(&contents) == header_len) {
                        if (is_eoc(header_len, &contents))
                                return looking_for_eoc;

                        if (header_len > 0 &&
                            CBS_data(&contents)[header_len - 1] == 0x80) {
                                /*
                                 * This is an indefinite length element. If
                                 * it's a SEQUENCE or SET then we just need to
                                 * write the out the contents as normal, but
                                 * with a concrete length prefix.
                                 *
                                 * If it's a something else then the contents
                                 * will be a series of DER elements of the same
                                 * type which need to be concatenated.
                                 */
                                const char context_specific = (tag & 0xc0)
                                    == 0x80;
                                char squash_child_headers =
                                    is_primitive_type(tag);

                                /*
                                 * This is a hack, but it sufficies to handle
                                 * NSS's output. If we find an indefinite
                                 * length, context-specific tag with a definite,
                                 * primitive tag inside it, then we assume that
                                 * the context-specific tag is implicit and the
                                 * tags within are fragments of a primitive type
                                 * that need to be concatenated.
                                 */
                                if (context_specific &&
                                    (tag & CBS_ASN1_CONSTRUCTED)) {
                                        CBS in_copy, inner_contents;
                                        unsigned int inner_tag;
                                        size_t inner_header_len;

                                        CBS_init(&in_copy, CBS_data(in),
                                            CBS_len(in));
                                        if (!cbs_nonstrict_get_any_asn1_element(
                                            &in_copy, &inner_contents,
                                            &inner_tag, &inner_header_len))
                                                return 0;

                                        if (CBS_len(&inner_contents) >
                                            inner_header_len &&
                                            is_primitive_type(inner_tag))
                                                squash_child_headers = 1;
                                }

                                if (!squash_header) {
                                        unsigned int out_tag = tag;

                                        if (squash_child_headers)
                                                out_tag &=
                                                    ~CBS_ASN1_CONSTRUCTED;

                                        if (!CBB_add_asn1(out,
                                            &out_contents_storage, out_tag))
                                                return 0;

                                        out_contents = &out_contents_storage;
                                }

                                if (!cbs_convert_indefinite(in, out_contents,
                                    squash_child_headers,
                                    1 /* looking for eoc */, depth + 1))
                                        return 0;

                                if (out_contents != out && !CBB_flush(out))
                                        return 0;

                                continue;
                        }
                }

                if (!squash_header) {
                        if (!CBB_add_asn1(out, &out_contents_storage, tag))
                                return 0;

                        out_contents = &out_contents_storage;
                }

                if (!CBS_skip(&contents, header_len))
                        return 0;

                if (tag & CBS_ASN1_CONSTRUCTED) {
                        if (!cbs_convert_indefinite(&contents, out_contents,
                            0 /* don't squash header */,
                            0 /* not looking for eoc */, depth + 1))
                                return 0;
                } else {
                        if (!CBB_add_bytes(out_contents, CBS_data(&contents),
                            CBS_len(&contents)))
                                return 0;
                }

                if (out_contents != out && !CBB_flush(out))
                        return 0;
        }

        return looking_for_eoc == 0;
}

int
CBS_asn1_indefinite_to_definite(CBS *in, uint8_t **out, size_t *out_len)
{
        CBB cbb;

        /*
         * First, do a quick walk to find any indefinite-length elements. Most
         * of the time we hope that there aren't any and thus we can quickly
         * return.
         */
        char conversion_needed;
        if (!cbs_find_indefinite(in, &conversion_needed, 0))
                return 0;

        if (!conversion_needed) {
                *out = NULL;
                *out_len = 0;
                return 1;
        }

        if (!CBB_init(&cbb, CBS_len(in)))
                return 0;
        if (!cbs_convert_indefinite(in, &cbb, 0, 0, 0)) {
                CBB_cleanup(&cbb);
                return 0;
        }

        return CBB_finish(&cbb, out, out_len);
}